Neuropeptides present in the hypothalamus play a major role in mediating the control of body weight. (Flier, et al., 1998. Cell, 92, 437-440.) Melanin-concentrating hormone (MCH) produced in mammals is a cyclic 19-amino acid neuropeptide synthesized as part of a larger pre-prohormone precursor in the hypothalamus which also encodes neuropeptides NEI and NGE. (Nahon, et al., 1990. Mol. Endocrinol. 4, 632-637; Vaughan, et al., U.S. Pat. No. 5,049,655; and Vaughan, et al., 1989. Endocrinology 125, 1660-1665.) MCH was first identified in salmon pituitary, and in fish MCH affects melanin aggregation thus affecting skin pigmentation. In trout and eels MCH has also been shown to be involved in stress induced or CRF-stimulated ACTH release. (Kawauchi, et al., 1983. Nature 305, 321-323.)
In humans two genes encoding MCH have been identified that are expressed in the brain. (Breton, et al., 1993. Mol. Brain Res. 18, 297-310.) In mammals MCH has been localized primarily to neuronal cell bodies of the hypothalamus which are implicated in the control of food intake, including perikarya of the lateral hypothalamus and zona inertia. (Knigge, et al., 1996. Peptides 17, 1063-1073.)
Pharmacological and genetic evidence suggest that the primary mode of MCH action is to promote feeding (orexigenic). MCH mRNA is up regulated in fasted mice and rats, in the ob/ob mouse and in mice with targeted disruption in the gene for neuropeptide Y (NPY). (Qu, et al., 1996. Nature 380, 243-247 and Erickson, et al., 1996. Nature 381, 415-418.) Injection of MCH centrally (ICV) stimulates food intake and MCH antagonizes the hypophagic effects seen with α melanocyte stimulating hormone (αMSH). (Qu, et al., 1996. Nature 380, 243-247.) MCH deficient mice are lean, hypophagic and have increased metabolic rate. (Shimada, et al., 1998. Nature 396, 670-673.) The administration of MCH has been indicated to be useful for promoting eating, appetite or the gain or maintenance of weight. (Maratos-Flier, U.S. Pat. No. 5,849,708.)
MCH action is not limited to modulation of food intake as effects on the hypothalamic-pituitary-axis have been reported. (Nahon, 1994. Critical Rev. in Neurobiol. 8, 221-262.) MCH may be involved in the body response to stress as MCH can modulate the stress-induced release of CRF from the hypothalamus and ACTH from the pituitary. In addition, MCH neuronal systems may be involved in reproductive or maternal function.
MCH can bind to at least two different receptors: MCH-1R and MCH-2R. (Chambers, et al., 1999. Nature 400, 261-265; Saito, et al., 1999. Nature 400, 265-269; Bächner, et al., 1999. FEBS Letters 457:522-524; Shimomura, et al., 1999. Biochemical and Biophysical Research Communications 261, 622-626; Sailer, et al., Proc. Natl. Acad. Sci. 98:7564-7569, 2001.) The amino acid identity between MCH-2R and MCH-1R is about 38%. (Sailer, et al., Proc. Natl. Acad. Sci. 98:7564-7569, 2001.)